This invention relates to an apparatus and method for controlling the emission, and recovery, of volatile solvents. In particular, this invention relates to a type of finish material applying apparatus which has become known as a robotized spraying cabinet and to methods of operating such an apparatus.
The application of finish materials to panels such as are used in the assembly of cabinets, office furniture, and so-called "knocked down" or KD furniture for residences is a well developed art. Much attention has been given to the development of finish materials themselves and to apparatus and methods of applying those materials. Many such finish materials are based on chemistry which uses volatile solvents as components of paint, lacquers, and other finishes. Such finish materials have been applied by spraying, by curtain flow, and in other manners.
One type of apparatus which provides a context for this invention is characterized by having an enclosed space (sometimes called a cabin) which is traversed by a conveyor on which panels or the like which are to receive finish materials are transported. Within the space is mounted a carousel head mounting a plurality of spray heads which are supplied with the finish materials to be applied and are rotated with the carousel head. Means, preferably in the form of some central processor control, are provided for sensing the configuration of the workpieces to be finished and the placement of the workpieces on the conveyor. In response to the sensed configuration and placement of a workpiece, the spray heads are activated to apply finish materials essentially only to the workpieces passing through the enclosed space. A flow of air is drawn or pushed through the area where finishing materials are applied in order to assist in controlling the emission of solvents and finishing materials.
It is known that apparatus of this general type may be constructed and operated without an enclosing cabinet or cabin and using spray heads which move about a circular path, an oval path, reciprocate, are fixed relative to conveyed workpieces, or move in other ways including being manually operated. Further, it is known that a variety of apparatus may be used in conveying workpieces through an area in which finishing materials are applied by spraying. It is contemplated that this invention, as described hereinafter, may be adapted to such alternative apparatus environments.
At least two problems with the emission of volatile solvents which form components of the finish materials arise in such an apparatus and method. One flows from the necessity, in order to assure full coverage of a workpiece with finish, of overspraying. That is, activation of a spray head must begin before the head traverses a workpiece and continue for at least a minimal distance beyond such traverse. Thus there is inevitably an overspray quantity of finish material released in the cabin and the volatile solvents contained in such materials may be easily vaporized and emitted into the ambient atmosphere.
The other of the two problems to be addressed here arises out of the need to clean the conveyor between passes through the cabin. More particularly, overspray of finish materials inevitably leads to deposition of such materials onto the conveyor and, if the conveyor continues uncleaned, to significant accumulation of such materials. With significant accumulation of finish materials on the conveyor, workpieces placed on the conveyor for transport would become stuck to the conveyor or otherwise contaminated with old finish materials, adversely affecting the quality of the finish applied. However, cleaning of the conveyor requires use of volatile solvents for the finishing system in use. Thus, any quantity of solvent retained for cleaning purposes is a source for evaporation into the ambient atmosphere.
The volatile solvents used in many finishing systems and materials have significant chemical and biological activity, such that governmental agencies concerned with the welfare of employees and the general public impose restrictions on the emission of such solvents. In order to assure that emissions are kept at or below required level, it is important to control such evaporation as has been described. Further, were the evaporation controlled (as proposed hereinafter), then the finish materials become available for recycling and reuse, thereby conserving the materials. As can be appreciated, as the solvent evaporates, the finish begins its drying and hardening. This is usually an irreversible process, especially if it takes the form of polymerization, as is often the case.